Data center is a center providing enterprise application business services, and is a center of data operations, exchange and storage. It integrates advanced network and storage technologies, carries more than 80% of service requests and data storage capacity of the network, and provides a service and operating platform for the healthy functioning of the customer service system.
In order to integrate the intranet and Ethernet, the concept of enhanced Ethernet is proposed. The enhanced Ethernet allows dividing different services, so that not only the needs of ordinary Ethernet but also the needs of the data center network can be met.
In the enhanced Ethernet, DCBX (Data Center Bridging Exchange Protocol) specifies auto-discovery and capability exchange protocol applied in the DCB (Data Center Bridging) device, and the DCB device applied in data center environments uses the protocol to directly exchange configuration information with the peer device which is directly connected with it, so as to configure the peer end device with the DCB function in the case that the peer end device allows. The protocol can also be used to detect non-matching configuration and configure the peer end device which is directly connected with it.
The DCBX function is not a new technology, it is an extension of the LLDP OUI TLV field, wherein LLDP is the Link Layer Discovery Protocol, OUI is the Organizationally Unique Identifier and TLV is the Type-Length-Value, in IEEE 802.1AB by the data center protocol, and carried in the LLDP packet for transmission.
The ETS is an improvement and enhancement of transmission selection entity capability of the output port. The ETS provides an operating model of priority processing and bandwidth allocation in the data center environment, through the use of ETS, different types of services such as LAN (Local Area Network), storage, clustering and management are divided into different traffic classes (referred to as TC) and provided with appropriate bandwidth allocation or best-effort services.
Each traffic class may comprise one or more priorities, all priorities which belong to the same traffic class share the bandwidth allocated to the traffic class, if the actually utilized bandwidth of the group is less than the bandwidth allocated to it, the idle bandwidth can be temporarily occupied by other traffics. Each traffic class can have its own priority queue scheduling algorithm. When using the DCBX to send the local-end ETS configuration, the standard provides two TLVs, one is configured TLV (Table 1) and the other is recommended TLV (Table 2). Wherein, the recommended TLV is configuration recommended to the peer end, and expects the peer end to configure the local device according to the current recommended configuration. The division of each traffic class in a packet, bandwidth information and scheduling algorithm can refer to Table 3, and each TC in Table 3 corresponds to 8 bits and is used to indicate the transmission selection algorithm used by the TC. Table 4 is a transmission selection algorithm description table.
TABLE 1ETS configured TLV formatTLVTLV802.1802.1WillingCB-SReservedMaxPriorityTCTransmissiontype =informationOUIsubtype = 9TCsassignmentbandwidthselection127string-00-80-tabletablealgorithmlength =c2(TSA)25assignmenttable7 bits9 bits3 octets1 octet1 bit1 bit3 bit3 bit4 octets8 octets8 octetsTLV headerTLV information string length = 25 bytes
The Willing bit in Table 1 indicates whether the local end is willing to accept the configuration of the peer end or not; the CBS bit indicates whether the device supports the Credit-based shaper scheduling algorithm or not; Max TCs indicates the maximum number of TCs that can be supported by the device.
TABLE 2ETS recommended TLV formatTLVTLV802.1802.1ReservedPriorityTCTransmissiontype = 127informationOUIsubtype =assignmentbandwidthselectionstring-00-80-10tabletablealgorithmlength =c2(TSA)25assignmenttable7 bits9 bits3 octets1 octet8 bits4 octets8 octets8 octetsTLV headerTLV information string length = 25 bytes
TABLE 3aPriority assignment tableByte1234Priority 0Priority 1Priority 2Priority 3Priority 4Priority 5Priority 6Priority 7Bit7430743074307430
TABLE 3bTC Bandwidth TableByte12345678TCTC % 1TC % 2TC % 3TC % 4TC % 5TC % 6TC % 7% 0
TABLE 3cTSA Assignment TableByte12345678Traf-TrafficTrafficTrafficTrafficTrafficTrafficTrafficficClass 1Class 2Class 3Class 4Class 5Class 6Class 7Class0
TABLE 4Transmission selection algorithm description tableTransmission Selection AlgorithmIdentifierStrict priority algorithm (8.6.8.1)0Credit-based shaper scheduling1algorithm (8.6.8.2)Enhanced Transmission Selection2Algorithm (8.6.8.3)Reserved3-254Vendor-specific transmission255 selection algorithm for DCBXVendor specifica four-byte integer, wherein threemost significant bytes hold the OUIvalue, and the value of the other sub-significant byte is an integer in therange of 0 to 255, and the integeris assigned by the OUI owner
By analyzing the abovementioned Table 2 to Table 4, it can be found that, since the ETS recommended TLV packet only carries the TC priority and bandwidth information, the protocol can only support priority-based scheduling algorithm, and cannot support guiding the traffic classes of the peer end in using a variety of scheduling algorithms. For other scheduling algorithms, especially those which need to perform weighted scheduling on the respective priorities, they are basically unable to meet the implementation, which likely results in the case that the low-priority queue is starved to death.